Type 1 diabetes (T1D) is thought to be a T-cell mediated auto-immune disease, where auto-aggressive CD4+ and CD8+ lymphocytes target and destroy the insulin producing pancreatic beta-calls. During the last decade, several studies have focused on different immune-based therapies to treat or prevent T1D. The aim of our proposed study is based on the idea that a combination of anti-CD3 systemic therapy with antigen specific approaches will result in a synergistic effect. We believe that anti-CD3 will act to 'reset' the immune system, thus opening a window for therapeutic interventions with antigen specific treatments to induce regulation that can maintain long-term tolerance in T1D. This approach will be tested pre-clinically, by using the NOD and RIP-LCMV transgenic mouse models treated with non-FcR binding anti-CD3 monoclonal antibody in combination with islet specific-antigens (administered as DNA, peptides or full protein), after recent onset of T1D. During this R21 phase, the optimal combination of antigen with non-FcR binding anti-CD3 will be identified. Studies will be carried out in these two mouse models to assess the effect of the immune intervention on antigen reactive T cells, and we will pursue the possibility, supported by our preliminary date, that regulatory cells are induced. In the ensuing R33 portion, we will conduct a 4-arm clinical trial, in which combinatorial therapy with anti-CD3 and antigen will be compared to intensive insulin therapy and observation in patients with recent onset diabetes. The trial will be conducted at Columbia and UCSF. Studies using samples from patients in this trial will be done to test the paradigms about regulator cells developed in the mice. This strategy will increase the efficacy of antigen specific immunizations by re-directing existing auto-reactive response and/or de novo induction of auto-antigen specific (adaptive) regulatory T cells. Furthermore, we propose that this effect of the combinatorial approach will allow us to maintain the clinical benefits by repeated administration of antigen.